Method of assembling a stator for an electric motor

ABSTRACT

The apparatus of the present invention provides a stator for an electric motor. The apparatus includes a plurality of stator components assembled together to form a generally annular stator core. A wire is wrapped around at least a portion of the stator core to form a stator winding. A first generally annular end plate and a second generally annular end plate are mounted to axially opposite sides of the stator core such that the stator core is axially trapped and retained therebetween. A fastener applies a clamping load to the first and second end plates such that the stator core is compressed therebetween. The clamping load from the fastener is applied directly to the first and second end plates which distribute the clamping load to the stator core such that the plurality of components are held together without the fastener directly applying the clamping load to the stator core. A corresponding method for providing a stator is similarly provided.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.11/402,541, filed Apr. 12, 2006, which is hereby incorporated byreference in its entirety.

TECHNICAL FIELD

The present invention pertains generally to a method and apparatus forassembling a stator of an electric motor.

BACKGROUND OF THE INVENTION

It is known to construct an electric motor using three or moreconcentrated windings wherein one or more of the windings are providedfor each of three electrical phases. These windings can distributemagnetic flux to multiple poles of the stator in the electric motor.Such a motor is three-dimensional, in that the magnetic flux passingthrough the concentrated winding is conducted both around thecircumference and along the axis of the motor in the stator.

Manufacturing and assembling a three-phase electric motor includesproducing a plurality of motor components having relatively complexgeometries, and performing additional processing steps such as, forexample, winding the stator wire around the stator core teeth in apredefined pattern. In an effort to reduce manufacturing costs, aplurality of component segments may be pre-formed and assembled togetherto produce the motor.

SUMMARY OF THE INVENTION

The apparatus of the present invention includes a plurality of statorcomponents composed of generally insulated ferromagnetic particles. Thestator components are assembled together to form a generally annularstator core. A wire is wrapped around at least a portion of the statorcore to form a stator winding. A first generally annular end plate and asecond generally annular end plate are mounted to axially opposite sidesof the stator core such that the stator core is axially trapped andretained therebetween. A fastener applies a clamping load to the firstand second end plates such that the stator core is compressedtherebetween. The clamping load from the fastener is applied directly tothe first and second end plates which distribute the clamping load tothe stator core such that the plurality of components are held togetherwithout the fastener directly applying the clamping load to the statorcore.

The plurality of stator components include a plurality of protrusionsand depressions adapted to facilitate the alignment of the statorcomponents as they are assembled to form the stator core.

The first and second end plates include a plurality of protrusionsand/or depressions adapted to facilitate the alignment of the first andsecond end plates relative to the stator core.

The apparatus of the present invention includes a first annular memberdisposed between the first end plate and the stator core, and a secondannular member disposed between the second end plate and the statorcore, wherein the first and second annular members are configured tomore evenly distribute the clamping load from the fastener to the statorcore.

The apparatus of the present invention includes an adhesive disposedbetween the first end plate and the stator core, and between the secondend plate and the stator core, wherein the adhesive is configured tohold the plurality of components together with a reduced fastenerclamping load.

The method of the present invention includes assembling the plurality ofstator components such that at least some of the alignment protrusionsand the alignment depressions engage to align the stator components andform a stator core. A wire is wrapped around at least a portion of thestator core to form a stator winding. The first and second end platesare mounted to axially opposite sides of the stator core such that thestator core is axially trapped and retained therebetween. A clampingload is applied to the first and second end plates with a fastener suchthat the stator core is compressed therebetween. The clamping load fromthe fastener is applied directly to the first and second end plateswhich distribute the clamping load to the stator core such that theplurality of components are held together without the fastener directlyapplying the clamping load to the stator core.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a stator assembly in accordance with thepresent invention;

FIG. 2 is a perspective view of a center segment of the stator assemblyof FIG. 1;

FIG. 3 is a perspective view of a sub-assembly of the stator assembly ofFIG. 1;

FIG. 4 is a perspective view of an end segment of the stator assembly ofFIG. 1; and

FIG. 5 is an exploded view of the stator assembly of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to the drawings, wherein like reference numbers refer to likecomponents, FIG. 1 shows a perspective view of a stator assembly 10 foran electric motor (not shown). In an effort to reduce manufacturingcosts, the stator assembly 10 includes a plurality of component segmentsthat are assembled together to produce the motor. More precisely, thestator assembly 10 includes a plurality of center segments 12 (i.e., sixidentical center segments which are attached together), at least onecoil winding 14, a plurality of end segments 16 (i.e., six identical endsegments which are attached together), a plurality of end plates 18, andat least one fastener such as the bolts or bars 80. The center segments12 and the end segments 16 are composed of pressure shaped ferromagneticparticles that are generally coated and insulated to provide lowelectrical conductivity. According to a preferred embodiment, theferromagnetic particles are a powdered metal composition which ispressed to form the shapes of the center segments 12 and the endsegments 16.

Referring to FIG. 2, a center segment 12 is shown in more detail. Thecenter segment 12 defines a front surface 24, a back surface 26 oppositethe front surface 24, and opposing end portions 28. The center segment12 also defines a radially outer shell portion 20 and a plurality ofteeth 22 extending therefrom. The teeth 22 each extend radially inwardfrom the shell portion 20 and terminate in a flanged end portion 32. Thecenter segment 12 includes a plurality alignment features such as, forexample, the alignment protrusions 34, the alignment depressions 35and/or the alignment depressions 36. To facilitate alignment, theprotrusions 34 and the depressions 36 are preferably generally conicalso as to allow for a margin of error during initial engagement andthereafter self-center to precisely align components during assembly;however, alternate alignment feature configurations may be envisioned.According to a preferred embodiment, the back surface 26 includes onealignment protrusion 34 and one alignment depression 36 and the frontsurface 24 includes three alignment depressions 35.

As shown in FIG. 3, two center segments 12 placed back-to-back (i.e., 26to 26), and a coil winding 14 are assembled together to form asub-assembly such as the sub-assembly 38, and thereafter threesub-assemblies 38, 38′ and 38″ are assembled together to form agenerally annular sub-assembly 42 as will be described in detailhereinafter.

The sub-assemblies 38, 38′ and 38″ each include two center segments 12such as the center segments 12′ and 12″ that are assembled together andhave multiple layers of wire 40 (shown schematically in FIG. 3) woundtherearound. The wire 40 wound about the respective center segments 12′and 12″ in the manner described hereinafter defines a coil winding 14for each respective sub assembly 38, 38′ and 38″. The two centersegments 12′ and 12″ are assembled by placing them back-to-back suchthat their respective back surfaces 26 (shown in FIG. 2) engage eachother. As the back surfaces 26 of the respective center segments 12 and12″ are brought together, the alignment protrusion 34 (shown in FIG. 2)of the center segment 12′ is insertable into an alignment depression 36(shown in FIG. 2) on the back of the center segment 12″, and thealignment protrusion 34 of the center segment 12″ is insertable into thealignment depression 36 on the back of the center segment 12′ such thatthe center segments 12′ and 12″ are aligned with each other. Thereafter,the wire 40 is wrapped around the teeth 22 of the center segments 12′and 12″ radially outwardly of the respective flanged end portions 32thereby forming a coil winding 14 and completing each respectivesub-assembly 38, 38′ and 38″. Each coil winding 14 is schematicallyshown as being generally rectangular; however, it should be appreciatedthat each winding 14 is actually composed of individual strands of wire40 wrapped around the teeth 22 multiple times. Three sub-assemblies 38,38′ and 38″ are positioned such that their respective end portions 28(shown in FIG. 2) engage or abut each other to form the generallyannular sub-assembly 42.

Referring to FIG. 4, one of the end segments 16 is shown in more detail.The end segment 16 defines an inner surface 50, an outer surface 52opposite the inner surface 50, and opposing end portions 54. The endsegment 16 also defines a radially outer housing portion 56 and aplurality of teeth 58 extending therefrom. The teeth 58 each extendradially inward from the housing portion 56 and terminate in a flangedend portion 60. The end segment 16 includes a plurality of alignmentfeatures such as the alignment protrusions 64. According to a preferredembodiment the inner surface 50 of each end segment 16 includes twoalignment protrusions 64 adapted to engage complimentary alignmentdepressions 35 of the sub-assembly 42 such that the end segment 16 isaligned relative thereto. Additionally, the outer surface 52 of each endsegment 16 includes two alignment protrusions 64 for alignment with anend plate 18. Three end segments 16 are positioned, preferably within afixture, such that their respective end portions 54 engage or abut as at55 (shown in FIG. 1) to form generally annular end rings 66 and 66′(shown in FIG. 5).

Referring to FIG. 5, the annular end plates 18 and 18′ are generallyO-shaped and each include a plurality of bolt holes 70. The end plates18, 18′ also include a plurality of alignment features such as thealignment depressions 72. The alignment depressions 72 each receive analignment protrusion 64 from one of the end rings 66 and 66″ such thatthe end plates 18, 18′ are respectively aligned relative thereto. Theend plates 18, 18′ are preferably composed of non-magnetic stainlesssteel; however, alternate compositions such as fiberglass reinforcedplastic may be envisioned.

Having identified the components of the stator assembly 10 hereinabove,the assembly steps will now be described with reference to FIG. 5showing an exploded view of the stator assembly 10. It should beappreciated that, unless otherwise specified, the assembly steps do notnecessarily have to be performed in the order described.

A first end plate 18 is located and retained, preferably in a fixture(not shown). A first end ring 66 composed of three end segments 16 isthen mounted to the first end plate 18. As the first end ring 66 ismounted to the first end plate 18, alignment protrusions 64 of the endring 66 are inserted into complementary alignment depressions 72 of theend plate 18 such that the first end ring 66 is aligned relative to thefirst end plate 18. The sub-assembly 42 which is assembled in the mannerdescribed hereinabove is then mounted to the first end ring 66. As thesub-assembly 42 is mounted to the first end ring 66, alignmentprotrusions 64 of the end ring 66 are inserted into complementaryalignment depressions 35 of the sub-assembly 42 such that thesub-assembly 42 is aligned relative to the first end ring 66. A secondend ring 66′ composed of three end segments 16 is then mounted to thesub-assembly 42. As the second end ring 66′ is mounted to thesub-assembly 42, alignment protrusions 64 of the end ring 66′ areinserted into complementary alignment depressions 35 of the sub-assembly42 such that the second end ring 66′ is aligned relative to thesub-assembly 42. A second end plate 18′ is then mounted to the secondend ring 66′. As the second end plate 18′ is mounted to the second endring 66′, alignment protrusions 64 of the second end ring 66′ areinserted into complementary alignment depressions 72 of the second endplate 18′ such that the second end ring 66′ is aligned relative to thesecond end plate 18′.

After the previously described components of the stator assembly havebeen aligned and assembled, preferably in a fixture (not shown), thefirst and second end plates 18 and 18′ are held together by a pluralityof fasteners such as the bolts or bars 80. The bolts 80 are configuredto pass axially through gaps formed between the teeth 22 and the teeth58 to retain the end plates 18 and 18′. The bolts 80 are preferablycomposed of a non-magnetic material such as non-magnetic stainless steelor titanium having low electrical conductivity to minimize eddy currentsin the bolts 80 caused by leakage flux.

The bolts 80 transmit a substantial clamping force through the endplates 18 and 18′ to retain the remaining components of the statorassembly 10. The clamping loads from the bolts 80 are initiallytransferred to the end plates 18 and 18′ which are configured to moreuniformly distribute such loads to the end rings 66, 66′ and thesub-assembly 42. The end plates 18 and 18′ are therefore composed of astronger material than that of the end rings 66, 66′ and thesub-assembly 42 which are preferably composed of powdered metal.Accordingly, the stronger end plates 18 and 18′ are adapted to adsorband distribute the relatively large clamping loads that hold the statorassembly 10 together, and to thereby protect the powdered metalcomponents from such loads.

For purposes of the present invention, the center segments 12 and theend segments 16 which are assembled together in the manner previouslydescribed define a generally annular stator core 84. In other words, thestator core 84 includes all the components of the stator assembly 10except the stator wire 40 and the coil windings 14, the end plates 18,and the bolts 80.

According to a preferred embodiment, a first annular member 90 isdisposed between the first end plate 18 and the first end ring 66, and asecond annular member 90′ is disposed between the second end plate 18′and the second end ring 66′. The annular members 90, 90′ are preferablycomposed of a pliable material such as that typically used for gaskets.The annular members 90, 90′ are adapted to prevent load spikes caused byirregularities in the end plates 18, 18′ or in the end rings 66, 66′,and to more uniformly distribute the loads applied by the bolts 80.

According to another preferred embodiment, adhesive 92 is disposedbetween the first end plate 18 and the first annular member 90, betweenthe annular member 90 and the first end ring 66, and/or between thefirst end ring 66 and the sub-assembly 42. Similarly, adhesive 92′ isdisposed between the sub-assembly 42 and the second end ring 66′,between the second end ring 66′ and the annular member 90′, and/orbetween the annular member 90′ and the end plate 18′. The adhesive 92,92′ acts to hold the stator assembly 10 together and thereby reduces therequisite bolt 80 clamping loads such that the powdered metal componentsdo not become damaged.

While the best modes for carrying out the invention have been describedin detail, those familiar with the art to which this invention relateswill recognize various alternative designs and embodiments forpracticing the invention within the scope of the appended claims.

1. A method for assembling a stator for an electric motor comprising:providing a plurality of stator components composed of generallyinsulated ferromagnetic particles, said plurality of stator componentsincluding a plurality of alignment protrusions and a plurality ofalignment depressions; assembling said plurality of stator componentssuch that at least a portion of said alignment protrusions and saidalignment depressions engage to align said plurality of statorcomponents and form a stator core; wrapping a wire around at least aportion of the stator core to form a stator winding; providing a firstgenerally annular end plate and a second generally annular end plate;mounting said first and second end plates to axially opposite sides ofsaid stator core such that said stator core is axially trapped andretained therebetween; applying a clamping load to the first and secondend plates with a fastener such that the stator core is compressedtherebetween; wherein said clamping load from said fastener is appliedto said first and second end plates which distribute the clamping loadto the stator core such that the plurality of components are heldtogether without said fastener directly applying the clamping load tothe stator core.
 2. The method of claim 1, wherein said providing afirst and second generally annular end plate includes providing a firstand second generally annular end plate having a plurality of projectionsand/or depressions configured to facilitate the alignment of the firstand second end plates relative to the stator core.
 3. The method ofclaim 2, further comprising providing a first annular member disposedbetween the first end plate and the stator core, and a second annularmember disposed between the second end plate and the stator core,wherein said first and second annular members are configured todistribute the clamping load from the fastener to the stator core. 4.The method of claim 2, further comprising providing an adhesive disposedbetween the first end plate and the stator core, and between the secondend plate and the stator core, wherein said adhesive is configured tohold the plurality of components together with a reduced fastenerclamping load.
 5. The method of claim 2, wherein said providing aplurality of stator components includes providing a plurality of centersegments and a plurality of end segments.